Cylindrospermopsis Raciborskii Research Articles

The impact of cell morphology and algal organic matter on algal floc properties

Physical floc properties were systematically investigated by analysing the structure of algal and cyanobacterial flocs produced by five species (green algae (Chlorella vulgaris) and cyanobacteria (Microcystis aeruginosa (strain CS-564), Microcystis aeruginosa (strain CS-555/01), Dolichospermum circinale and Cylindrospermopsis raciborskii) using aluminium sulphate (alum) at different doses and pH values. The properties of spherical, compact flocs were determined using a laser diffraction instrument and a new in situ image analysis technique was validated to analyse the structure of more complex flocs. The incorporation of algal-derived organic matter (AOM) into the flocs was inferred by evaluating the dissolved organic matter concentration character before and after flocculation using liquid chromatography with organic carbon detection (LC-OCD). D. circinale, C. raciborskii, and M. aeruginosa (CS-564) produced large flocs (2–9 mm), while M. aeruginosa (CS-555) and C. vulgaris produced smaller flocs (<2 mm). While differences in physical floc properties were observed to result from changes in coagulation mechanism, the cell morphology and the AOM composition were the most influential factors. Examination of floc properties can give a rapid insight at the plant for trouble shooting, particularly through the use of the in situ techniques and provide a mechanism by which floc properties can be tailored to downstream processes.

Low invasion success of an invasive cyanobacterium in a chlorophyte dominated lake

Biological invasions are a major threat to biodiversity and ecosystem functioning. Successful invasions depend on the interplay of multiple abiotic and biotic factors, however, the process of the invasion itself is often overlooked. The temporal variation of environmental factors suggests that a ‘window of opportunity’ for successful invasions exists. Especially aquatic habitats, like temperate lakes, undergo pronounced seasonal fluctuations and show temporally varying environmental conditions in e.g. nutrient availability, temperature and the composition of the resident community including competitors and consumers. We experimentally tested if an invasion window for the globally invasive cyanobacterium Cylindrospermopsis raciborskii exists. From May to September, we determined the invasion success of C. raciborskii in laboratory mesocosms with natural lake water. Although the invasion success was generally low, the invasiveness varied among months and differed in total invasive biomass, net development and final share of C. raciborskii in the community. During the first days, C. raciborskii strongly declined and this initial, short-term decline was independent of the ambient consumptive pressure. These results are in contrast to laboratory studies in which C. raciborskii successfully invaded, suggesting that a complex natural system develops a resistance to invasions.

Cyanobacterial biodiversity of semiarid public drinking water supply reservoirs assessed via next-generation DNA sequencing technology.

Next-generation DNA sequencing technology was applied to generate molecular data from semiarid reservoirs during well-defined seasons. Target sequences of 16S-23S rRNA ITS and cpcBA-IGS were used to reveal the taxonomic groups of cyanobacteria present in the samples, and genes coding for cyanotoxins such as microcystins (mcyE), saxitoxins (sxtA), and cylindrospermopsins (cyrJ) were investigated. The presence of saxitoxins in the environmental samples was evaluated using ELISA kit. Taxonomic analyses of high-throughput DNA sequencing data showed the dominance of the genus Microcystis in Mundaú reservoir. Furthermore, it was the most abundant genus in the dry season in Ingazeira reservoir. In the rainy season, 16S-23S rRNA ITS analysis revealed that Cylindrospermopsis raciborskii comprised 46.8% of the cyanobacterial community in Ingazeira reservoir, while the cpcBAIGS region revealed that C. raciborskii (31.8%) was the most abundant taxon followed by Sphaerospermopsis aphanizomenoides (17.3%) and Planktothrix zahidii (16.6%). Despite the presence of other potential toxin-producing genera, the detected sxtA gene belonged to C. raciborskii, while the mcyE gene belonged to Microcystis in both reservoirs. The detected mcyE gene had good correlation with MC content, while the amplification of the sxtA gene was related to the presence of STX. The cyrJ gene was not detected in these samples. Using DNA analyses, our results showed that the cyanobacterial composition of Mundaú reservoir was similar in successive dry seasons, and it varied between seasons in Ingazeira reservoir. In addition, our data suggest that some biases of analysis influenced the cyanobacterial communities seen in the NGS output of Ingazeira reservoir.

Characteristics of Phytoplankton Community and Its Relationship with Environmental Factors in Different Regions of Yilong Lake, Yunnan Province, China

Yilong Lake, a shallow, plateau lake, is the ninth largest water body in the Yunnan Province, China. In order to figure out the characteristics of phytoplankton communities in different regions of this lake, the phytoplankton and environmental factors in the west region, east region, and in a submerged macrophytes restoration demonstration region were monthly investigated and analyzed from August 2013 to July 2014. The results showed that the habitats in different regions were spatially heterogeneous. Total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH4+-N), five-day biochemical oxygen demand (BOD5), transparency (SD), turbidity (Turb.), and electrical conductivity (EC) had no significant differences between the demonstration region and the west region, but these two regions showed significant differences in comparison with the east region (P<0.05). The largest phytoplankton density was Cyanophyta and the dominant species in the three regions were different. Mersmopedia tenuissima had the highest dominance in the west region; Cylindrospermopsis raciborskii and Pseudanabaena limntica were the most dominant taxa in the east region; while Merismopedia tenuissima and Anabaenopsis sp. were dominant in the O. uminata restoration demonstration region. PCoA compared the β diversity of phytoplankton communities in the three different regions based on the entire year investigations. It was found that the community structures of the west region and O. uminata restoration demonstration region were similar (P>0.05), but they were significantly different from the community from the east region (P<0.01). Redundant analysis (RDA) showed that TN, TP, BOD5, and SD were the main environmental factors affecting the distribution of phytoplankton community in Yilong Lake. In addition, NH4+-N, EC, permanganate index, and pH also have a certain effect on the phytoplankton community.

Removal efficiency of phosphorus, cyanobacteria and cyanotoxins by the “flock & sink” mitigation technique in semi-arid eutrophic waters

Geoengineering techniques have been used to control phosphorus and cyanobacteria in lakes promising greater and quicker chemical and ecological recovery. Techniques that use coagulants and clays to remove particulates and dissolved phosphorus from the water column have received great. In this study, bench-scale “flock & sink” assays were carried out to evaluate the efficiency of the coagulants aluminium sulphate (SUL), polyaluminium chloride (PAC) and chitosan (CHI), alone and combined with natural bentonite clays (BEN) and lanthanum-modified bentonite (LMB), to remove of phosphorus from a eutrophic reservoir in a semi-arid region of Brazil. In addition, the study seeks to assess the effects on the cyanobacteria density and the intra- and extracellular concentrations of cyanotoxins after the application of these geoengineering materials. The SUL and PAC coagulants effectively reduced the total phosphorus (TP), reactive soluble phosphorus (SRP), turbidity, chlorophyll-a, cyanobacteria density and intracellular microcystin, whereas CHI showed a low removal efficiency. Lanthanum-modified bentonite proved to be more effective than BEN; however, the application of the coagulants only was sufficient to successfully remove phosphorus and cyanobacteria from the water column. In addition, the efficiency of the “flock & sink” technique in cell removal varied among the cyanobacteria species. Small colonial species such as Aphanocapsa delicatissima, Merismopedia glauca and Merismopedia tenuissima were removed regardless of the treatment used, including those with CHI and BEN. As for the filamentous cyanobacteria, Cylindrospermopsis raciborskii, Geitlerinema amphibium, Planktothrix agardhii and Pseudanabaena catenata, removal was achieved only using PAC, SUL and LMB alone or when combined. The intracellular concentrations of saxitoxin and cylindrospermopsin and the extracellular fraction of these cyanotoxins and of microcystin were not influenced by the application of coagulants and clays. This indicates that cell lysis did not occur with the addition of the geoengineering materials. These results demonstrate that the “flock & sink” technique could be used for restoration of eutrophic waters.

Acclimation at high temperatures increases the ability of Raphidiopsis raciborskii (Cyanobacteria) to withstand phosphate deficiency and reveals distinct strain responses

ABSTRACT Raphidiopsis (Cylindrospermopsis) raciborskii is one of the most studied potentially harmful cyanobacteria. Single environmental factors such as increased temperature or light are reported to be promoters of R. raciborskii growth, but the interaction of two or more promoting factors is less understood. The performance of two strains of R. raciborskii (MVCC19, Uruguayan and LP1, Brazilian) were evaluated under acclimation and temperature shifts (25–32°C) in combination with two transitions from phosphorus (P) sufficiency to limiting growth conditions. When subjected to transition from high P sufficiency to a P-limiting state, strains were able to grow only at the warmer temperature if previously acclimated. The MVCC19 strain showed higher specific growth rates and a shorter growth phase than LP1. Morphological differences were also found: the MVCC19 strain produced shorter filaments, while the LP1 strain increased in length and the number of cells per filament. The results show the positive effect of high temperature on the ability of R. raciborskii to withstand P-limiting conditions, which may confer resilience of populations to periods of severe nutrient limitation in warm lakes. This finding contributes to the understanding of the success of this species in diverse environmental conditions. The effect of temperature on the tolerance of nutrient deficiency and the performance of strains under lake conditions suggests the need for a drastic reduction in nutrient loads to avoid R. raciborskii dominance in warmer lakes.

Nutritional and toxicity constraints of phytoplankton from a Brazilian reservoir to the fitness of cladoceran species.

Camorim is a small, eutrophic reservoir in Rio de Janeiro, Brazil, with a phytoplankton community dominated most of the year by the filamentous diatom Aulacoseira spp. and the toxic cyanobacterium Cylindrospermopsis raciborskii. As filamentous species can be a poor food for grazers, we hypothesize that phytoplankton from this reservoir would constrain cladoceran fitness due to nutritional limitation and/or toxicity when animals fed mixtures of cultured green algae and natural seston. Clones of different cladoceran species were exposed either to seston from Camorim reservoir sampled in different seasons or to a C. raciborskii strain (CYLCAM-2) isolated from the reservoir. In short-term assays, cladocerans were exposed to either 100% seston or mixtures of 50% seston added to green algae (200μg CL-1), and their survivorship and somatic growth were measured for 4days. In life table assays, neonates were exposed to the same seston treatments over 14days and age at first reproduction, survivorship, fecundity, total offspring, and the intrinsic rate of natural increase (r) were assessed. In general, seston negatively affected cladoceran survivorship and fitness (r), but this response was seasonally and species specific. Stronger effects of CYLCAM-2 than those caused by seston on survivorship, somatic growth, and r were found for all cladoceran species, especially when the proportion of CYLCAM-2 was higher than 50% in relation to green algae in a fixed total food concentration. Our results suggest that both nutritional (C/P and morphology) and toxicity factors can act to impair cladoceran fitness and help explain the absence of cladocerans in Camorim reservoir.

Bioaccumulation of microcystins in seston, zooplankton and fish: A case study in Lake Zumpango, Mexico

Cyanotoxins from toxic blooms in lakes or eutrophic reservoirs are harmful to several organisms including zooplankton, which often act as vectors of these secondary metabolites, because they consume cyanobacteria, bioaccumulate the cyanotoxins and pass them on along the food chain. Microcystins are among the most commonly found cyanotoxins and often cause zooplankton mortality. Although cyanobacterial blooms are common and persistent in Mexican water bodies, information on the bioaccumulation of cyanotoxins is scarce. In this study we present data on the bioaccumulation of cyanotoxins from Planktothrix agardhii, Microcystis sp., Cylindrospermopsis raciborskii and Dolichospermum planctonicum blooms in the seston (suspended particulate matter more than 1.2 μm) by zooplankton and fish (tilapia (Oreochromis niloticus) and mesa silverside (Chirostoma jordani) samples from Lake Zumpango (Mexico City). The cyanotoxins were extracted from the seston, zooplankton and fish tissue by disintegration using mechanical homogenization and 75% methanol. After extraction, microcystins were measured using an ELISA kit (Envirologix). Concentration of microcystins expressed as equivalents, reached a maximum value of 117 μg g-1 on sestonic samples; in zooplankton they were in the range of 0.0070-0.29 μg g-1. The dominant zooplankton taxa included Acanthocyclops americanus copepodites, Daphnia laevis and Bosmina longirostris. Our results indicate twice the permissible limits of microcystins (0.04 μg kg-1 d-1) for consumption of cyanobacterial products in whole fish tissue of Chirostoma jordani. The data have been discussed with emphasis on the importance of regular monitoring of water bodies in Mexico to test the ecotoxicological impacts of cyanobacterial blooms and the risk that consumption of products with microcystins could promote.

Impacts of Different Phosphorus Contents on the Growth of Cylindrospermopsis raciborskii in the Aquatic Environment

Background: Cyanobacteria are the most important group of algae. Many factors are involved in the rapid growth of algae such as phosphorus and nitrogen contents. Objectives: The current study aimed at evaluating the effect different phosphorus concentrations on the growth rate of Cylindrospermopsis raciborskii during the aquatic life. Methods: The experiment was carried out for 12 days at three phosphorus concentrations and one control group in Zehnder 8 and Blue-Green 11 media. The rates of cell division per day (G) and specific growth rate (µ) were separately estimated for each group. Cyanobacterium was tested at three phosphorus concentrations; 150, 300, and 600 µg/L. Results: The current study results showed that increasing phosphorus concentration had a significant effect on the growth of C. raciborskii in some particular days of cultivation. The maximum growth rate (0.9 per day) was observed at 7 g/L phosphorus concentration. Conclusions: Phosphorus was a limiting factor and contributed to the removal of toxins from the alga and its blooming. The maximum growth rate was observed in the group treated on the day 8 of cultivation with phosphorus concentration of 300 µg/L.

Ecological meta-analysis of bloom-forming planktonic Cyanobacteria in Argentina

The aim of the present research was to summarize the main reasons that explain the distribution of harmful blooms of cyanobacteria in Argentina. It is a large territory with climates ranging from humid tropical to cold temperate. We performed a meta-analysis of the published data and information in technical reports published from 1945 to 2015, and included additional data from personal non-published studies. A total of 122 water bodies affected by planktonic cyanobacterial blooms were recorded and geo-referenced. The analysis showed that blooms, defined as events exceeding 5000 cells/mL, occurred in different types of water bodies, including shallow lakes, rivers, streams, reservoirs, estuaries and storage facilities. Maximum bloom abundance and species and ecological strategies (dispersive, scum-forming, nitrogen fixer) responsible for each event were related to the geographic and climatologic characteristics and type and origin of water bodies. The Puna and the Andean Patagonia eco-regions were mostly free of blooms. The most impaired aquatic systems were shallow lakes and reservoirs (46.7 and 24.6%, respectively). Deep lakes had no reports of blooms and rivers were mainly affected at the regulated reaches, with intensities generally decreasing downstream the dams. Besides, 74.3% of the blooms reported in Argentina exceeded WHO Alert Level 2 for drinking and bathing waters (100,000 cells/mL). Thirty-nine species, identified by Komárek’s polyphasic approach to taxonomy, were responsible for the blooms. Microcystis aeruginosa, Dolichospermum spiroides, Dolichospermum circinale, Raphidiopsis mediterranea and Cylindrospermopsis raciborskii were frequently found participating in either mixed or single species blooms. The species distribution was associated with the eco-region and aquatic system typologies and affected by seasonality and climatological and geographic variables. The eco-strategies of cyanobacterial species showed stronger associations with the qualitative and quantitative indicators used in the meta-analysis, and appeared as useful tools for management measures.

Combined Effect of Light and Temperature on the Production of Saxitoxins in Cylindrospermopsis raciborskii Strains.

Cylindrospermopsis raciborskii is a potentially toxic freshwater cyanobacterium that can tolerate a wide range of light and temperature. Due to climatic changes, the interaction between light and temperature is studied in aquatic systems, but no study has addressed the effect of both variables on the saxitoxins production. This study evaluated the combined effect of light and temperature on saxitoxins production and cellular quota in C. raciborskii. Experiments were performed with three C. raciborskii strains in batch cultures under six light intensities (10, 40, 60, 100, 150, and 500 μmol of photons m−2 s−1) and four temperatures (15, 20, 25, and 30 °C). The growth of C. raciborskii strains was limited at lower temperatures and the maximum growth rates were obtained under higher light combined with temperatures equal or above 20 °C, depending on the strain. In general, growth was highest at 30 °C at the lower light intensities and equally high at 25 °C and 30 °C under higher light. Highest saxitoxins concentration and cell-quota occurred at 25 °C under high light intensities, but were much lower at 30 °C. Hence, increased temperatures combined with sufficient light will lead to higher C. raciborskii biomass, but blooms could become less toxic in tropical regions.

Quantifying the role of organic phosphorus mineralisation on phytoplankton communities in a warm-monomictic lake

ABSTRACTPhosphorus (P) is a key driver of phytoplankton growth in lentic systems. During summer-stratified periods when dissolved inorganic P (DIP) is low, the phytoplankton assemblage often has elevated P uptake rates. Under these conditions, dissolved organic P (DOP) can become an important source of P for phytoplankton and a driver of phytoplankton succession. We examined how DOP mineralisation by alkaline phosphatase (AP) activity (APA), relative to phytoplankton P release (i.e., from exudation and lysis), meets phytoplankton P uptake and how it is associated with phytoplankton community composition changes under thermally stratified DIP-depauperate conditions in a large warm-monomictic lake. We found that when phytoplankton internal P stores were low (<0.65 µg P µg−1 Chl-a), APA increased, resulting in potential DOP mineralisation rates of 88 µg L−1 h−1 P, which is at the upper end of rates in the literature. APA represented up to 89% of the total phytoplankton P uptake and was much higher than the rate of phytoplankton P release. We found that elevated APA coincided with peak phytoplankton biovolume and dominance of the phytoplankton assemblage by cyanobacteria. Further, APA was strongly positively associated with the majority of the 10 most dominant cyanobacteria, including the key toxin-producer Raphidiopsis raciborskii (previously Cylindrospermopsis raciborskii). Our results indicate that under DIP-depauperate conditions, DOP mineralised by APA may be a major source of P for phytoplankton, and the ability to produce AP may be a key factor in the occurrence of bloom-forming cyanobacteria.

Toxic effects and energy distribution characteristics of photosynthetic system II(PSII) in &lt;i&gt;Cylindrospermopsis raciborskii&lt;/i&gt; exposed to heavy metal cadmium

为了研究重金属镉对藻类光合系统毒性效应及能量分配特征，以拟柱孢藻（Cylindrospermopsis raciborskii）为研究对象，分析了不同镉浓度下拟柱孢藻的生长、单位叶绿素a含量、光合系统II（PSII）叶绿素荧光及其能量分配模型.结果表明：不同浓度镉培养拟柱孢藻96 h后，0.2 mg/L Cd2+对拟柱孢藻单位细胞叶绿素a含量及PSII活性无显著影响，而0.5 mg/L Cd2+培养时拟柱孢藻的单位细胞叶绿素a含量为对照组的62.97%.当Cd2+浓度高于5 mg/L时，拟柱孢藻的PSII活性受到抑制并导致表征量子产额分配的φEo和ψo分别下降了15.35%和13.52%.此外，当Cd2+浓度高于5 mg/L时，藻体PSII能量分配表现为TRO/CSm和ETO/CSm显著减小，DIO/CSm差异不显著，类囊体能量分配表现为ABS/RC、TRO/RC和DIO/RC显著增大，明显区别于0.2、0.5和1 mg/L Cd2+处理组.这些结果表明PSII反应中心是镉对拟柱孢藻光合作用影响的重要作用位点，且Cd2+高于5 mg/L时显著影响了拟柱孢藻PSII反应中心并且抑制了PSII电子传递链供体侧的电子传递，而拟柱孢藻则可能通过改变PSII的能量分配来保护和缓解镉对其光合结构的损伤.

Species Diversity of Algae of the Kiev Upland Rivers (Ukraine)

The results of the study of algal flora in 12 rivers (Ros, Stugna, Krasna, Rosava, Uzynka, Rokytka, Siverka, Kozynka, Bobrytsia, Bezimenna, Gorokhovatka, and Protoka) of the Kiev Upland Region are presented. In total, according to original data 493 species (511 infraspecies taxa = ist) were identified. Bacillariophyta (39.8%) and Chlorophyta (27.8%) form the core of the taxonomic structure followed by Euglenophyta (10.7%) and Cyanoprokaryota (9.3%). Other divisions of algae were less diverse. Studied rivers differ in species number: algal flora of the Ros River was the richest while the Bobrytsia River was the lowest in algal diversity. A comparison of floristic resemblance in species composition of algae by means of the Serensen-Chekanovsky coefficient showed three pairs of rivers with the greatest degree of similarity, which included the Ros and the Stugna rivers (0.41), the Siverka and the Bezimenna (0.40), and the Protoka and the Uzynka (0.36) rivers. According to the literature and original data, a systematic list was compiled, which include 545 species (572 ist) which belong to 10 divisions, 15 classes, 41 orders, 91 families and 201 genera. In the studied rivers, a number of new and noteworthy taxa were found. Encyonema neomesianum Krammer (= Encyonema minutum var. pseudogracilis (Cholnoky) D.B. Czarnecki) and Navicula microrhombus (Cholnoky) Schoeman et Archibald are first cited for Ukraine. Amphora inariensis Krammer, Cylindrospermopsis raciborskii (Wolosz.) Seenayya et Subba Raju, Craticula subminuscula (Manguin) Wetzel et Ector (= Eolimna subminuscula (Manguin) Gerd Moser, Lange-Bertalot et Metzeltin), Diploneis elliptica (Kutz.) Cleve, Eunotia crista-galli Cleve, Navicula erifuga Lange-Bert., Stephanodiscus neoastraea Hakansson et Hickel, S. parvus Stoermer et Hakansson, and Radiococcus planktonicus J.W.G. Lund are new records for the Middle Dnieper Algofloristic Subprovince. Noteworthy records for this region include Cyclotella atomus Hustedt, Discostella pseudosteligera (Hustedt) Houk et Klee, Gomphonema laticollum E. Reichardt, Fallacia subhamulata (Grunow) D.G. Mann, Navigeia decussis (0strup) Bukht., Planktolyngbya contorta (Lemmerm.) Anagn. et Komarek, Pseudanabaena redekei (Goor) B.A. Whitton (= Limnothrix redekei (Van Goor) Meffert.), Pseudostaurosira subconstricta (Grunow) Kulokovskiy et Genkal, Staurosira construens var. subsalina (Hust.) Gerasimiuk, Staurosira binodis (Ehrenb.) Lange-Bertalot, S. venter (Ehrenb.) Cleve et J.D. Moller, Stephanodiscus delicatus Genkal, Staurosirella pinnata (Ehrenb.) D.M. Williams et Round, and Surirella librile (Ehrenb.) Ehrenb. The taxonomic list for algae of the Kiev Upland Region rivers are added; it includes both original and revised literature data. New and noteworthy records are illustrated by original microphotographs.

Cianobacterias en un embalse subtropical de la provincia de Salta (Argentina)

El embalse Limón se ha convertido en la principal fuente de agua potable para el 80% de la población del norte de la provincia de Salta (22° 05’47,90’’S-63° 44’ 19,48’’ W). Al presente, no existe información sistematizada de las algas del fitoplancton presentes en esta presa. Se analizaron 19 muestras del período 2013-2015 en ambas fases del ciclo hidrológico, según técnicas estandarizadas, con el objeto de evaluar la representatividad de cianobacterias potencialmente tóxicas en Limón y su importancia relativa en el fitoplancton. Existió un predominio de cianobacterias, con un incremento interanual significativo, siendo éstas más abundantes en los estiajes, con un promedio de 110.160 células en 2015, con predominio de Cylindrospermopsis raciborskii y Raphidiopsis mediterranea (75.027 y 170.000 células/ml). Entre las especies con potencial toxicogénico se destacaron por sus densidades Anabaenopsis elenkinii, Aphanizomenon gracile, Aphanocapsa annulata, Coelomoron tropicale, Chroococcus dispersus, C. raciborskii, Microcysis flos-aquae, Planktolyngbia limnetica, Pseudanabaena limnetica, R. mediterránea y R. curvata. La representatividad del grupo dentro del fitoplancton fue superior al 70 %. Se concluye que el cuerpo de agua es un ambiente de riesgo y debe ser monitoreado permanentemente para su empleo para agua de consumo humano.

Distribution and Factors Affecting Cylindrospermopsis raciborskii in Guangdong Reservoirs

Cylindrospermopsis raciborskii originating from tropical and subtropical regions is potentially toxic and attracts much attention due to its extension to the global temperate zone in recent years. Based on historical data of 20 reservoirs with different trophic levels (dry season, wet season, and transitional season of 2010), this study focuses on the analysis of the occurrence and distribution of C. raciborskii in the Guangdong Province. Based on the results, C. raciborskii was found in 19 of the 20 reservoirs and its biomass ranges from 0.0001-39.740 mg·L-1 and accounts for 0.02%-97.07% of the total phytoplankton biomass. Both a notable spatial and seasonal distribution of C. raciborskii were observed. Its occurrence is higher in the western coastal area (77.78%) than in the Zhujiang Delta (66.67%) and northern coastal area (33.33%) and is relatively lower in the dry season (40%) compared with the rainy season (70%) and transition season (85%). The trophic level has a significant effect on the presence of C. raciborskii, which is notably higher in eutrophic reservoirs (81.48%) than in mesotrophic reservoirs (66.67%) and oligotrophic reservoirs (33.33%). The redundancy analysis shows that C. raciborskii biomass is positively correlated with total nitrogen (TN) and the trophic state index (TSI) and negatively correlated with dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), and the secchi depth (SD). Thus, C. raciborskii in Guangdong reservoirs may be promoted by environmental factors such as high nitrogen contents, low phosphorus concentration, and transparency.

Application of N-TiO2 for visible-light photocatalytic degradation of Cylindrospermopsis raciborskii — More difficult than that for photodegradation of Microcystis aeruginosa ?

Nowadays Cylindrospermopsis raciborskii (C. raciborskii) and the metabolites produced, such as cylindrospermopsin (CYN), pose a serious threat to the ecosystem. Advanced oxidation technologies have been verified as constituting a very promising means to eliminate the risk from harmful algae. But so far little research has focused on the visible-light photocatalytic destruction of C. raciborskii cells and the degradation of their metabolites.In our study, N-doped TiO2 (N-TiO2) was used to degrade C. raciborskii and the degradation was compared with that of the Microcystis aeruginosa (M. aeruginosa). Results showed that although the photodegradation of C. raciborskii was more difficult than that of M. aeruginosa, the treatment with N-TiO2 was still satisfactory. After adding 200 mg/L N-TiO2, C. raciborskii cells (5 × 106 cells/mL) were completely destroyed within 20 h under visible light irradiation, and nearly 90% of the organic matter and CYN in the suspensions were also degraded, thereby markedly improving the water quality.The photocatalytic process starts with damage to the cell membrane resulting in the leakage of internal components. Subsequently, the leaked metabolites were oxidised by the reactive oxidizing species produced by N-TiO2. Thus, the application of N-TiO2 is a promising method for the treatment of C. raciborskii.

Is the presence of Central European strains of Raphidiopsis (Cylindrospermopsis) raciborskii a threat to a freshwater fish? An in vitro toxicological study in common carp cells

As yet European strains of Raphidiopsis raciborskii (previously Cylindrospermopsis raciborskii) have not been found to produce known cyanotoxins although their extracts have caused adverse effects in mammals, as shown using in vitro and in vivo experimental models. The present study investigated whether R. raciborskii isolated from Western Poland and Ukraine can affect fish cells using in vitro exposures of hepatocytes and red blood cells (RBC), and brain homogenates obtained from common carp (Cyprinus carpio) to 1.0% and 0.1% extracts of 7 strains. The studied extracts evoked different responses of catalase activity in hepatocytes with both increase and decrease observed under low and high concentrations. The cellular thiol pool was also altered with most extracts inducing a decrease in the activity of glutathione-S-transferase, and Ukrainian strains leading to an increase in glutathione level and a decrease in metallothionein content. All the studied extracts induced comparable reactive oxygen species formation, lipid peroxidation, protein carbonylation and DNA fragmentation in hepatocytes, and all but one increased the activity of caspase-3. Only one extract caused lysosomal membrane destabilization as measured by neutral red retention in RBC. In contrast to extracts of Ukrainian isolates, exposure of brain homogenates to extracts of Polish strains induced an increase in acetylcholinesterase activity suggesting the neurotoxic action of their exudates. The results indicate that both Polish and Ukrainian strains of R. raciborskii may pose a toxicological risk to freshwater fish, and further, that Polish strains may produce compound(s) evoking neurotoxic effects.

Cylindrospermopsis raciborskii Virus and host: genomic characterization and ecological relevance.

Cylindrospermopsis (Raphidiopsis) raciborskii is an invasive, filamentous, nitrogen-fixing cyanobacterium that forms frequent blooms in freshwater habitats. While viruses play key roles in regulating the abundance, production and diversity of their hosts in aquatic ecosystems, the role(s) of viruses in the ecology of C. raciborskii is almost unexplored. Progress in this field has been hindered by the absence of a characterized virus-host system in C. raciborskii. To bridge this gap, we sequenced the genome of CrV-01T, a previously isolated cyanosiphovirus, and its host, C. raciborskii strain Cr2010. Analyses suggest that CrV-01T represents a distinct clade of siphoviruses infecting, and perhaps lysogenizing, filamentous cyanobacteria. Its genome contains unique features that include an intact CRISPR array and a 12 kb inverted duplication. Evidence suggests CrV-01T recently gained the ability to infect Cr2010 and recently lost the ability to form lysogens. The cyanobacterial host contains a CRISPR-Cas system with CRISPR spacers matching protospacers within the inverted duplication of the CrV-01T genome. Examination of metagenomes demonstrates that viruses with high genetic identity to CrV-01T, but lacking the inverted duplication, are present in C. raciborskii blooms in Australia. The unique genomic features of the CrV/Cr2010 system offers opportunities to investigate in more detail virus-host interactions in an ecologically important bloom-forming cyanobacterium.

A Greek Cylindrospermopsis raciborskii strain: Missing link in tropic invader’s phylogeography tale

The cyanobacterium Cylindrospermopsis raciborskii represents a challenge for researchers and it is extensively studied for its toxicity and invasive behaviour, which is presumably enhanced by global warming. Biogeography studies indicate a tropical origin for this species, with Greece considered as the expansion route of C. raciborskii in Europe. The widening of its geographic distribution and the isolation of strains showing high optimum growth temperature underline its ecological heterogeneity, suggesting the existence of different ecotypes. The dominance of species like C. raciborskii along with their ecotoxicology and potential human risk related problems, render the establishment of a clear phylogeography model essential. In the context of the present study, the characterization of Cylindrospermopsis raciborskii TAU-MAC 1414 strain, isolated from Lake Karla, with respect to its phylogeography and toxic potential, is attempted. Our research provides new insights on the origin of C. raciborskii in the Mediterranean region; C. raciborskii expanded in Mediterranean from North America, whilst the rest of the European strains may originate from Asia and Australia. Microcystin synthetase genes, phylogenetic closely related with Microcystis strains, were also present in C. raciborskii TAU-MAC 1414. We were unable to unambiguously confirm the presence of MC-LR, using LC–MS/MS. Our results are shedding light on the expansion and distribution of C. raciborskii, whilst they pose further questions on the toxic capacity of this species.